Ferris, Richard. [from old catalog] · New York, T. Nelson and sons · leaf 19
A biplane glider Aeroplanes exist in several types: the monoplane,with one spread of surface; the biplane, with twospreads, one above the other; the triplane, with threespreads, or decks; the multiplane, with more thanthree.2 18 INTRODUCTORY. The tetrahedral plane is a structure of many smallcells… … Helicopter is used to designate machines whichare lifted vertically and sustained in the air by pro-p€>llers revolving in a horizontal plane, as distin-guished from the propellers of the aeroplane, whichrevolve in vertical planes. INTRODUCTORY. 19 A parachute is an umbrella-like contrivance…
Aeronautics
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